Storage Devices

Categories of Media

Four Categories of storage media:

  • Magnetic media
    • Hard Disks and Tapes
  • Non-volatile memory (flash)
  • Optical media.

Partitioning and Slack Space

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Interfaces

SATA (Serial Advanced Technology Attachment)

  • Versions/Speeds
    • 1.5 Gb/s for SATA 1
    • 3.0 Gb/s for SATA 2
    • 6 Gb/s (~700MB/s) for SATA 3
    • 16 Gb/s for SATA 3.2
  • has card-edge connector

SAS (Serial Attached SCSI)

  • Versions/Speeds
    • 3 Gb/s for SAS 1
    • 6 Gb/s for SAS 2
    • 12 Gb/s for SAS 3
    • 22.5 Gb/s for SAS 4
  • Same connector/interface as SATA, but has separator

SCSI (Small Computer System Interface)

  • aka Scuzzy
  • up to 320 Mb/s
  • SCSI-2: 50-pin interface, Molex power
  • SCSI-3: 68-pin interface, Molex power
  • SCSI-3 variant: 80-pin interface

IDE (Integrated Drive Electronics) aka PATA

  • 133 Mb/s
  • has pin connector
  • 40-position connector; 39-pin interface
  • IDE drive jumper options
    • Master
    • Slave
    • Cable select
    • Note original jumper setting prior to imaging
  • Standard power connector

HDD Disk Parts/Design

HDD Sizes

HDDs has 3 storage sizes:

  • 3.5 in
  • 2.5 in
  • 1.8 in

Components

Parts of a drive:
**cf_hdd

Disk Data Structure

Platters

  • round flat, magnetic or ceramic discs in a hard drive that holds the actual data
    • Made of two materials
      • Substrate Material
      • Magnetic Media Coating
    • Each platter has two sides
      • sides are numbered starting at 0
    • Most drives have multiple platters

Tracks

  • Each platter has tracks, which is where data is stores

    • Most platters have 10k+ tracks
    • Track numbering start at 0 from the outside
    • Stacks of tracks are called cylinders

  • Number of cylinders (tracks), heads (sides), and sectors (aka CHS) uniquely identify the physical geometry of the storage units on a disk

    • CHS also yields disk capacity:
    • Capacity = Cylinders x Heads x Sectors x sector size
    • Pasted image 20260116134011.png

  • Trend toward less platters with more density

Sectors

  • Each track has sectors
    • 1 sector = 512 bytes (sometimes 4096) and a few extra "info bits"
      • Info bits include ID info, synchronization fields, and ECC data.
    • Sectors can turn bad beacuse of:
      • excessive read/writes
      • some viruses
      • voltage surges
    • Drives have reserved sectors, which are used as others fail
    • bad sectors are difficult to see by normal operating systems, requires special hardware

Fragmentation

  • Data on HDDs can be spread out, called fragmentation.
  • Fragmentation increases seek time/delay

SSD Parts/Design

Components

  • SSDs use flash based storage and a controller

Advantages over HDDs

  • Constant seek time
  • No file fragmentation issues
  • No moving parts
    • no mechanical failures
    • fast startup time
    • no motor noise
  • Lighter weight
  • low power

Issues

  • Overwriting process is complicated & expensive
    • read-erase-modify-write cycle
  • Cells have limited life/cycles
    • Wear leveling must be used
  • SSDs are significantly harder to save data from

SSD Data storage structure

  • 1 page = 8 sections/sectors (512 bytes)
  • Pages make up blocks
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Data writing process

  • Write is fast
  • But rewrite/overwrite involves additional erasing step
  • Entire Blocks (not pages or sections) must be erased
  • Pasted image 20260117000152.png
  • Grey = unused page
  • blue = in-use page
  • Optimization strategies
    • Pasted image 20260117000904.png
  • Garbage collection
    • Pasted image 20260117001023.png

SSD Lifespan

  • Individual memory cells have limited read/write cycles (5000 – 50000)
  • Like hard disks SSDs have extra capacity not accessible by normal users
  • Unlike hard disks Approx. 10-25% more storage than stated capacity, Overprovisioned areas are continuously used

TRIM

  • File Deletion on a normal HDD
    • File is marked as deleted in the File system’s database
    • HDD has no clue which sectors are freed up
    • TRIM marks data blocks as stale
  • SSDs need to know this info.
    • Modern OS have support for this command